Partial combustion or gasification of coal involves reacting the coal at elevated temperatures and possibly elevated pressures with a limited volume of oxygen, the reaction preferably being carried out in the presence of additional agents such as steam, carbon dioxide, or various other materials. Gasification of coal produces a gas, known as synthesis gas, that contains mostly carbon monoxide and hydrogen. Also produced are varying quantities of other gases, such as carbon dioxide and methane, and various liquid and solid materials, such as small particles of ash and carbon commonly known and collectively defined herein as flyslag or flyash. This flyslag, because it is derived from a "reducing" atmosphere, tends to be different in composition and properties from flyash normally associated with combustion boilers where a fully oxidizing atmosphere is utilized. For example, the flyslag from processes for partial combustion of a coal may contain elemental iron, sulphides and deposited carbon, components not normally associated with boiler flyash. In general, the flyslag or ligher flyash entrained with the gas in partial combustion processes is usually removed from the raw synthesis gas by a combination of cyclones or separators, or a water scrubbing system employing washer coolers, venturi scrubbers, or filters or electrostatic precipitators, or combinations of these systems.
The raw synthesis gas from the gasifier or gasification zone contains, in addition to the aforementioend materials, sulfur-containing gases, such as hydrogen sulfide and carbonyl sulfide, as well as small amounts of inorganic metal sulfides. The presence of these inorganic metal sulfides as vaporized materials and small fines in synthesis gas derived from the gasification of coal complicates removal of additional impurities such as H.sub.2 S and/or CO.sub.2, and poses problems insofar as product quality and pollution control requirements are concerned.
The flyslag or flyash removed from the synthesis gas have heretofore generally been considered to have undesirable properties insofar as its ultimate disposal is concerned. For example, it may be light, friable, dusty and difficult to compact. Because it may contain unsuitable species such as arsenic, selenium, and sulfides, it must be handled with care, and, if it is to be utilized or disposed of as landfill, must be in a form which does not release such materials readily to the environment. The invention addresses the problem of flyslag utilization, concomitantly accomplishing the treatment and utilization of other nominal inorganic metal sulfide lighter weight waste products from the gasification process.